1. Field of the Invention
The present invention relates to an ultrasound unit for the clinical application of hyperthermia to tumor cells in soft tissues.
2. Background Art
Ultrasound units for the destruction of cells are known per se, from GB-A No. 820814. These are primarily designed for use in surgery and operate to totally destroy all tissue at the point of acoustic focus.
It is known that ultrasound is useful in raising tissue temperature to values typically between 42.degree. and 48.degree. C., but to higher temperatures if desirable. In the lower part of this range healthy tissue is able to dissipate the heat by virtue, inter alia, of arterial dilation and hence may remain comparatively undamaged. Necrosed and neoplastic tissues, however, have a limited, non-existent or non-elastic blood supply, and hence overheat. This causes selective death of these tissues. Even at the peripheral edges of a tumor where blood supply tends to be disproportionally high, the lack of arterial dilation assists in the death of these tissues.
It has been known, for example, from the British Journal of Cancer 1982 Vol. 45 Supplement V. P68-70 to provide an array of radially disposed sonic transducers which provide intersecting beams of sonic energy spaced some 50 mm into a model target, i.e. at the point of acoustic focus. When this array was used on a liver tissue sample with normal blood flow, it was found that maximum temperature was not obtained at the acoustic focus because, it is believed, blood supply to the intervening healthy tissue reduced the temperature increase.
However, as may be seen from Radiation & Environment Biophysics, Vol. 19, P215-266 1981, tumor tissue has varying densities and blood flow characteristics. Non-uniform temperature distribution in practice occurs, therefore, and this leads to the well perfused regions of tumor tissue escaping effective treatment.